Nanoscale structures such as nanoparticles and nanotubes have unique physiochemical properties. Their extremely high surface area, for example, provides many advantages over conventional particles with dimensions in the micron scale. Carbon nanotubes additionally exhibit extraordinary thermal conductivity and unique mechanical and electrical properties.
Because of their unique properties, nanoscale structures have many diverse uses. For example, metal nanoparticles are attractive for environmental remediation of various contaminants. Various chlorinated aliphatic hydrocarbons and toxic metals can be remediated using metal nanoparticles such as zero valent iron (Fe0) nanoparticles (known as FeNP or nZVI—nanoscale zero valent iron). Metal nanoparticles have also been used for the remediation of groundwater contaminated with chemicals used in explosives. The effectiveness of a remediation approach depends on various factors, one of which is the ability to access the contaminant(s) with the metal nanoparticles. Fe0 nanoparticles, for example, are highly reactive and react rapidly with surrounding media in the subsurface (dissolved oxygen and/or water, for example). Thus, significant loss of reactivity can occur before the particles are able to reach the target contaminant.
For effective bioremediation and a variety of applications, it is necessary to individually disperse and suspend the nanoparticles in a liquid medium. One of the most important liquid mediums is water since it is inexpensive and non-toxic. Due to the high density of many nanoparticles and strong interparticle surface interactions, suspension of nanoparticles in water is challenging. Metal nanoparticles, such as Fe0 nanoparticles, tend to flocculate or aggregate when added to water due to interparticle van der Waal interactions. Flocculation and aggregation reduce the effective surface area of the metal and cause precipitation or sedimentation of the metal from the aqueous phase.
WO2009/111722 (Bezbaruah et al., published 11 Sep. 2009) describes metal nanoparticles entrapped in or surface-modified with an amphiphilic polysiloxane graft copolymer (APGC). The resultant nanoparticle exhibits increased colloidal stability, reduced oxidation by non-target compounds, and affinity toward water/contaminant interfaces. However, the copolymer is not sufficiently biodegradable to render the nanoparticle delivery vehicles described therein suitable for all environmental applications.